The present invention relates to a communication system for multicast distribution, and more particularly to a communication system that is equipped with a multicast adaptive translator device and performs multicast address translation of IPv4-IPv6.
A content distribution service using multicast in the Ipv4 network has been recently founded. Furthermore, a network based on the IPv6 network has been also expanded because of a so-called address depletion problem, etc. When the same service as the content distribution service provided in the IPv4 network is provided in the IPv6 network, it is necessary to provide the same multicast server to the IPv6 network. At this time, it is expected that the multicast server is not provided to each of the IPv4 network and the IPv6 network, but a multicast server which overstrides both the IPv4 and IPv6 is developed.
Therefore, when a client in the IPv6 network views/listens to a content of a multicast server of the IPv4 network or a client in the IPv4 network views/listens to a content of a multicast server of the IPv6 network, it is necessary to perform multicast packet translation in a multicast adaptive translator as in the case of an unicast packet.
JP-A-2001-285357 has proposed a system of statically pre-registering IPv4-IPv6 multicast group addresses in an address translation table of the translator. According to this system, the multicast communication is carried out by carrying out multicast address translation with a pre-registered multicast server. That is, according to this publication, an IPv6 multicast packet from a multicast server connected to the IPv6 network is translated into a pre-registered virtual IPv4 multicast group address, and then the multicast packet is transmitted to a multicast client connected to the IPv4 network.
Furthermore, there have been also proposed protocols such as Internet Group Management Protocol (IGMPv3) and Multicast Listener Discovery (MLDv2) in which a multicast client can indicate plural multicast server addresses (source addresses) for one multicast group address as disclosed in RFC2236 (IGMPv2), RFC2710 (MLDv1), RFC3376 (IGMPv3) and RFC3810 (MLDv2).